Not applicable.
This invention relates in general to compositions of matter and, more particularly, to polymerizable adhesive compositions that include a cationically polymerizable component, an acidic component, and an initiator capable of initiating cationic polymerization. These compositions may also include a polyol and/or a free radically polymerizable component. The polymerizable compositions of the present invention are useful for a variety of applications, including use as adhesives for bonding to hard tissue and cationically curable or cured restorative materials.
Dental compositions such as composites, sealants, and cements generally will not bond sufficiently to tooth enamel or dentin unless the enamel or dentin is pretreated with an adhesive layer, etchant, and/or primer. Typically, the tooth is etched with an acidic solution, and optionally, this is followed by application of a (meth)acrylate-based pre-adhesive composition that is polymerized using a redox, chemically or photochemically activated free radical initiator to form a layer of adhesive. The dental composition, which is typically a filled (meth)acrylate-based composition, is then placed over the adhesive and polymerized using a free radical initiator system to form a hard, wear-resistant material. The adhesive, therefore, bonds to both the acid-etched tooth and to the dental composition.
(Meth)acrylate-based dental compositions exhibit a relatively high degree of volumetric shrinkage upon polymerization. Accordingly, cationically curable compositions, and hybrid compositions featuring both cationically and free radically curable components, have been suggested as alternatives. Such compositions, which typically include epoxy resins as the cationically curable component, exhibit less shrinkage upon cure than compositions that are made predominately of (meth)acrylate. If such cationically curable components are to be used, the pre-adhesive used to bond such components may contain a substantial number of cationically curable TID groups. However, pre-adhesive compositions containing relatively large amounts of cationically curable groups that have previously been disclosed do not bond well to hard tissues, such as tooth enamel and dentin, because the hard tissue inhibits polymerization of such materials.
An epoxide/polyol polymeric composition that includes a photoinitiator system comprising an iodonium salt, a visible light sensitizer, and an electron donor compound is disclosed by one of the present inventors, with another, in U.S. Pat. No. 5,998,495 (the ""495 patent). The ""495 patent further suggests that other cationically polymerizable polymers can be incorporated into the epoxide/polyol polymeric composition. U.S. Pat. No. 6,025,406 (the ""406 patent) discloses an epoxide polymeric composition that includes a photoinitiator system comprising an iodonium salt, a visible light sensitizer, and an electron donor compound.
U.S. Pat. No. 5,980,253 discloses treating hard tissues by applying a composition that includes a cationically active functional group, a free radically active functional group, and a polymerization initiator capable of initiating free radical polymerization. However, the disclosure specifies that the amount of cationically active functional group present is no greater than about 0.0075 moles per gram of composition.
PCT Application No. PCT/US97/08534 discloses dental compositions comprising a polymerizable component, an acid reactive filler, a hydrophilic component, a polymerization initiator, and an acid. PCT Application No. PCT/US96/16299 discloses dental compositions comprising a polymerizable component, a fluoride-releasing material, a hydrophilic component, a polymerization initiator, and an acid.
Despite the advances resulting from the above-noted polymeric compositions, a need still exists for cationically polymerizable compositions having adhesive properties to hard tissues. Still further, these adhesive compositions should be able to successfully polymerize on the surface of hard tissue to form a strong bond with the hard tissue, yet at the. same time, they should successfully bond to subsequently applied compositions that include cationically active groups.
The present invention is directed to an adhesive composition that includes a mixture of a cationically polymerizable component, an acidic component, and an initiator capable of initiating cationic polymerization. Preferably, the initiator comprises an iodonium salt, a visible light sensitizer, and an electron donor compound, wherein the initiator has a photoinduced potential greater than or equal to that of N,N-dimethylaniline in a standard solution of 2.9xc3x9710xe2x88x925 moles/g diphenyl iodoniun hexafluoroantimonate and 1.5xc3x9710xe2x88x925 moles/g camphorquinone in 2-butanone. This adhesive composition is cationically polymerizable and is able to bond to hard tissue and cationically curable or cured restorative materials.
Additional novel features and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the compositions particularly pointed out in the appended claims.
The present invention is directed to an adhesive composition comprising a cationically polymerizable component, an acidic component, and an initiator capable of initiating cationic polymerization. These components are mixed to form the adhesive composition. These components may be sold unmixed so that the composition can be made just prior to use. The composition results in a polymerized product when one or more of the cationically polymerizable components in the composition are contacted with the initiator under conditions sufficient to promote polymerization ofthe component. This adhesive composition may also include a compound having a reactive olefinic moiety (an unsaturated aliphatic hydrocarbon functional group), a free radically polymerizable component, a polyol, or combinations thereof.
Any cationically polymerizable component or combinations thereof may be used in the adhesive composition of the present invention. As used herein, a xe2x80x9ccationically polymerizable componentxe2x80x9d refers to a compound having a cationically active functional group. This cationically active functional group is a chemical moiety that is activated in the presence of an initiator capable of initiating cationic polymerization such that it is available for reaction with other compounds bearing cationically active functional groups. Examples of cationically polymerizable components include, but are not limited to, epoxy resins, vinyl ethers, oxetanes, spiroothrocarbonates, spiroorthoesters, and combinations thereof. Spiroorthocarbonates are esters of orthocarboxylic acid and have four oxygen atoms bonded to a single carbon atom, with the carbon atom being common to two ring systems.
Epoxy resins have an oxirane ring, which is polymerizable by ring opening. Epoxy resins include monomeric epoxy compounds and epoxides of the polymeric type and can be aliphatic, cycloaliphatic, aromatic or heterocyclic. Epoxy resins generally have, on the average, at least 1 polymerizable epoxy group per molecule, preferably at least about 1.5 and more preferably at least about 2 polymerizable epoxy groups per molecule. The polymeric epoxides include linear polymers having terminal epoxy groups (e.g., a diglycidyl ether of a polyoxyalkylene glycol), polymers having skeletal oxirane units (e.g., polybutadiene polyepoxide), and polymershaving pendent epoxy groups (e.g., a glycidyl (meth)acrylate polymer or copolymer). The epoxides may be provided by one compound or may be mixtures of compounds containing one, two, or more epoxy groups per molecule. The average number of epoxy groups per molecule is determined by dividing the total number of epoxy groups in the epoxy-containing material by the total number of epoxy-containing molecules present.
These epoxy-containing materials may vary from low molecular weight monomeric materials to high molecular weight polymers and may vary greatly in the nature of their backbone and substituent groups. For example, the backbone may be of any type and substituent groups thereon can be any group that does not substantially interfere with cationic polymerization at room temperature. Illustrative of permissible substituent groups include halogens, ester groups, ethers, sulfonate groups, siloxane groups, nitro groups, phosphate groups, and the like. The molecular weight of the epoxy-containing materials may vary from about 58 to about 100,000 or more.
Useful epoxy-containing materials include those which contain cyclohexene oxide groups such as epoxycyclohexanecarboxylates, typified by 3,4-epoxycyclohexylmethyl-3,4 epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexane carboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate. For a more detailed list of useful epoxides of this nature, reference is made to the U.S. Pat. No. 3,117,099.
Further epoxy-containing materials which are useful in the compositions of this invention include glycidyl ether monomers. Examples are glycidyl ethers of polyhydric phenols obtained by reacting a polyhydric phenol with an excess of chlorohydrin such as epichlorohydrin (e.g., the diglycidyl ether of 2,2-bis-(2,3-epoxypropoxyphenol)-propane). Further examples of epoxides of this type are described in U.S. Pat. No. 3,018,262, and in Handbook of Epoxy Resins by Lee and Neville, McGrawv-Hill Book Co., New York (1967).
There are a host of commercially available epoxy resins which can be used in this invention. In particular, epoxides which are readily available include octadecylene oxide, epichlorohydrin, styrene oxide, vinyl cyclohexene oxide, glycidol, glycidylmethacrylate, diglycidyl ether of Bisphendl A (e.g., those available under the trade designations Epon 828(trademark), Epon 825(trademark). Epon 1004(trademark) and Epon 1010(trademark) from Shell Chemical Co., and DER-333(trademark), DER-332(trademark), and DER-334(trademark), from Dow Chemical Co.), vinylcyclohexene dioxide (e.g., ERL-4206(trademark) from Union Carbide Corp.), 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate (e.g., ERL-4221(trademark) or CYRACURE UVR 6110(trademark) or UVR 6105(trademark) from Union Carbide Corp.), 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methyl-cyclohexene carboxylate (e.g., ERL-420(trademark) from Union Carbide Corp.), bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate (e.g., ERL-4289(trademark) from Union Carbide Corp.), bis(2,3-epoxycyclopentyl)ether (e.g., ERL-0400(trademark) from Union Carbide Corp.), aliphatic epoxy modified from polypropylene glycol (e.g., ERL-4050(trademark) and ERL-4052(trademark) from Union Carbide Corp.), dipentene dioxide (e.g., ERL-4269(trademark) from Union Carbide Corp.), epoxidized polybutadiene (e.g., Oxiron 2001(trademark) from FMC Corp.), silicone resin containing epoxy functionality, flamne retardant epoxy resins (e.g., DER-580(trademark), a brominated bisphenol type epoxy resin available from Dow Chemical Co.), 1,4-butanediol diglycidyl ether of phenolformaldehyde novolak (e.g., DEN-431(trademark) and DEN-438(trademark) from Dow Chemical Co.), resorcinol diglycidyl ether (e.g., Kopoxite(trademark) from Koppers Company, Inc.), bis(3,4-epoxycyclohexyl)adipate (e.g., ERL-4299(trademark) or TVR-6128(trademark), from Union Carbide Corp.), 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-metadioxane (e.g., ERL-4234(trademark) from Union Carbide Corp.), vinylcyclohexene monoxide 1,2-epoxyhexadecane (e.g, UVR-6216(trademark) from Union Carbide Corp.), alkyl glycidyl ethers such as alkyl C8-C10 glycidyl ether (e.g., HELOXY Modifier 7(trademark) from Shell Chemical Co.), alkyl C12-C14 glycidyl ether (e.g., HELOXY Modifier 8(trademark) from Shell Chemical Co.), butyl glycidyl ether (e.g., HELOXY Modifier 61(trademark) from Shell Chemical Co.), cresyl glycidyl ether (e.g., HELOXY Modifier 62(trademark) from Shell Chemical Co.), p-terbutylphenyl glycidyl ether (e.g., HELOXY Modifier 65(trademark) from Shell Chemical Co.), polyfunctional glycidyl ethers such as diglycidyl ether of 1,4-butanedol (e.g., HELOXY Modifier 67(trademark) from Shell Chemical Co.), diglycidyl ether of neopentyl glycol (e.g., HELOXY Modifier 68(trademark) from Shell Chemical Co.), diglycidyl ether of cyclohexanedimethanol (e.g., HELOXY Modifier 107(trademark) from Shell Chemical Co.), trimethylol ethane triglycidyl ether (e.g., HELOXY Modifier 44(trademark) from Shell Chemical Co.), trimethylol propane triglycidyl ether (e.g., HELOXY Modifier 48(trademark) from Shell Chemical Co.), polyglycidyl ether of an aliphatic polyol (e.g., HELOXY Modifier 84(trademark) from Shell Chemical Co.), polyglycol diepoxide (e.g., HELOXY Modifier 32(trademark) from Shell Chemical Co.), diglycidyl ether of bisphenol F (e.g., Araldite(trademark) GY-281(trademark) from Ciba-Geigy Corp.), and 9,9-bis[4-(2,3-epoxypropoxy-phenyl]fluorenone (e.g., Epon 1079(trademark) from Shell Chemical Co.).
Still other epoxy resins contain copolymers of acrylic acid esters or glycidol such as glycidylacrylate and glycidylmethacrylate with one or more copolymerizable vinyl compounds. Examples of such copolymers are 1:1 styrene glycidylmethacrylate, 1: 1 methyl methacrylate-glycidylacrylate and a 62.5:24:13.5 methyl methacrylate-ethyl acrylate-glycidylmethacrylate.
Other useful epoxy resins are well known and contain such epoxides as epichlorohydrin; alkylene oxides, such as propylene oxide, styrene oxide, and/or butadiene oxide; and glycidyl esters, such as ethyl glycidate.
The polymers of the epoxy resin can optionally contain other functionalities that do not substantially interfere with cationic polymerization at room temperature. Blends of various epoxy-containing materials are also contemplated. Examples of such blends include two or more weight average molecular weight distributions of epoxy-containing compounds, such as low molecular weight (below 200), intermediate molecular weight (about 200 to 10,000). and higher molecular weight (above about 10,000). Alternatively or additionally, the epoxy resin may contain a blend of epoxy-containing materials having different chemical natures, such as aliphatic and aromatic, or functionalities, such as polar and non-polar.
Epoxy resins that preferably are used as the cationically polymerizable resin include diglycidyl ether of bisphenol F obtained from Ciba Geigy under the tradename Araldite(trademark) GY 281; diglycidyl ether of bisphenol A obtained from Shell Chemical Co. under the tradename Epon 825; 3xe2x80x2,4xe2x80x2-epoxycyclohexanemethyl-3,4-epoxycyclohcxane carboxylate obtained from Union Carbide under the tradename Cyracure(trademark) UVR 6105; trimethyol propane triglycidyl ether obtained from Shell Chemical Co. under the tradename Heloxy 48; butanediol diglycidyl ether obtained from Ciba Geigy under the tradename RD 2; and bis(3,4-epoxycyclohexylmethyl)adipate obtained from Union Carbide under the tradename ERL 4299. The preferred epoxy resins for providing physical strength and integrity to the cured adhesive composition are made of diepoxide monomers.
Vinyl ethers that may be used as the cationically polymerizable resin include, but are not limited to, tri(ethylene glycol)divinyl ether (TEGDVE), glycidyl vinyl ether (GVE), butanediol vinyl ether (BDVE), di(ethylene glycol)divinyl ether (DEGDVE), 1,4-cyclohexanedimethanol divinyl ether (CHDMDVE), 4-(1-propenyloxymethyl)-1,3-dioxolan-2-one (POMDO), 2-cloroethyl vinyl ether (CEVE), or 2-ethylhexyl vinyl ether (EHVE), ethyl vinyl ether (EVE), n-propyl vinyl ether (NPVE), isopropyl vinyl ether (IPVE), n-butyl vinyl ether (NBVE), isobutyl vinyl ether (IBVE), octadecyl vinyl ether (ODVE), cyclohexyl vinyl ether (CVE), butanediol divinyl ether (BDDVE), hydroxybutyl vinyl ether (HBVE), cyclohexanedimethanol monovinyl ether (CHMVE), tert-butyl vinyl ether (TBVE), tert-amyl vinyl ether (TAVE), dodecyl vinyl ether (DDVE), ethylene glycol divinyl ether (EGDVE), ethylene glycol monovinyl ether (EGMVE), hexanediol divinyl ether (HDDVE), hexanediol monovinyl ether (HDMVE), diethylene glycol monovinyl ether (MVE-2), triethyleneglycol methyl vinyl ether (MTGVE), tetraethylene glycol divinyl ether (DVE-4), trimethylolpropane trivinyl ether (TMPTVE), aminopropyl vinyl ether (APVE), poly-tetrahydrofuran divinyl ether (PTHFDVE), pluriol-E200 divinyl ether (PEG200-DVE), n-butyl vinyl ether (n-BVE), 4-hydroxybutylvinylether (HBVE), ethylene glycol butyl vinyl ether (EGBVE), 2-diethylaminoethyl vinyl ether (DEAEVE), dipropropylene glycol divinyl ether (DPGDVE), octadecyl vinyl ether (ODVE), a vinyl ether terminated aromatic ester monomer, a vinyl ether terminated aliphatic ester monomer, a vinyl ether terminated aliphatic urethane oligomer, and a vinyl ether terminated aromatic urethane oligomer.
The acidic components that are used in making the adhesive composition of the present invention are compounds having acidic.or acidogenic functional groups that also have adhesion properties. An acidogenic group is a group that can generate an acid, such as an anhydride or an acid halide. Any of four classes of acidic components or combinations thereof may be used in making the adhesive composition of the present invention. Preferably, the acidic component is a compound that also contains a reactive olefinic moiety.
The first class of acidic components is maleic anhydride and its ring-opened derivatives that have at least one acid or acidogenic functionality. The following structures show ring-opened derivatives resulting from the reaction product of maleic anhydride with an alcohol or a primary or secondary amine to form an ester or an amide, as shown below: 
wherein R1, R2, R3, and R4 are independently selected from any aliphatic or aromatic radical. As the basicity of R1, R2, R3, or R4 increases, the rate of cationic polymerization, using one of the reaction products shown above as the acidic component, slows down. A substituent on the acidic component that slows down the rate of cationic polymerization may be chosen to control the reaction rate. However, the selection of a substituent so basic that it stops the polymerization reaction should be avoided. If R1, R2, R3, or R4 is an aliphatic or aromatic radical, then preferably it is an organic radical containing a free radically polymerizable group. Most preferably, the free radically polymerizable group is (meth)acrylate. Examples of suitable components in this class are maleic acid, maleic anhydride, 2-(methacryloyloxy)ethyl maleate (MAEM), and the reaction products of maleic anhydride and 2-hydroxyethylacrylate, 2-hydroxyethylmethacrylate (HEMA), 2- and 3-hydroxypropylacrylate and methacrylate, 1,3- and 2,3-dihydroxypropylacrylate and methacrylate, 2-hydroxypropyl-1,3-diacrylate and dimethacrylate, 3-hydroxypropyl-1,2diacrylate and dimethylacrylate, pentaerythritol diacrylate and dimethacrylate, 2-aminoethylacrylate, 2-aminoethylmethacrylate, 2- and 3-aminopropylacrylate and methacrylate, 1,3- and 2,3-diaminopropylacrylate and methacrylate, 2-aminopropyl-1,3-diacrylate and dimethacrylate, and 3-aminopropyl-1,2-diacrylate and dimethylacrylate. These reaction products have the structures of the compounds shown above.
The second class of acidic components is polymeric polycarboxylic acids of the formula: 
wherein each R is independently selected from H, CH3, or CH2CO2H and n can be any integer so long as the acid is at least partially soluble in the other components of the adhesive composition sufficient so as to provide enhanced adhesion. This second class of acidic components also includes copolymers that include the polycarboxylic acid described above and a free radically polymerizable group. Preferably, the acid has a number average molecular weight that is less than about 10,000. More preferably, the number average molecular weight is less than about 5,000. Even more preferably, the number average molecular weight is less than about 3,000. Examples of suitable components in this class are homopolymers and copolymers of acrylic acid (AA), methacrylic acid, and itaconic acid (IA). Ifpoly(acrylic acid) is used, preferably, it has a molecular weight of about 2,500.
The third class of acidic components is compounds of the formula: 
wherein each R1, R2, and R3 of compound (1) and R4 of compound (2) are independently selected from any aliphatic or aromatic radical that does not interfere with cationic polymerization. At least two of the substituents, RI, R2, and R3 of compound (1), each must contain at least one polymerizable group such as free radically polymerizable groups. One of the substituents of compound (1) can be hydrogen. R4 of compound (2) must contain at least two polymerizable groups. R1, R2, and/or R3 may be (meth)acryloyl substituted polycarboxylic acids. Examples of acids that fall into this third category are tartaric acid or citric acid that has been functionalized with at least two ethylenic functionalities. For example, citric acid may be ethylenically functionalized by substituting with an acryloyl or methacryloyl functionality. These polymerizable groups may be attached directly to the acid containing compound or may be optionally attached through a linking group. Preferred linking groups include substituted or unsubstituted alkyl, alkoxyalkyl, aryl, aryloxyalkyl, alkoxyaryl, aralkyl or alkaryl groups. Particularly preferred linking groups comprise an ester functionality and most particularly preferred linking groups comprise an amide functionality. Most preferably, the radical is alkyl or dialkyl aminoethyl (meth)acrylate or hydroxyethyl (meth)acrylate. These are compounds having an acidic group and two unsaturated groups per molecule. An example of a suitable acidic component in this class is 2-({N-[2-(2-methylprop-2-enoyloxy)ethyl]carbamoyloxy}methyl)-3-[N-(2-prop-2-enoyloxyethyl)carbamoyloxy] propanoic acid (PDMA).
The fourth class of acidic components is compounds of the formula: 
wherein R is an alkyl group having 2 to 4 carbons or a cycloalkyl group having 5 to 6 carbons, each M is independently selected from hydrogen, metal ions, complex organic cations such as tetraalkylanmuonium salts, and alkyl groups, and each n is an integer independently selected from 1 to 4. If M is a metal cation, preferably, it is sodium or potassium. Examples of suitable compounds in this class are ethylenediamine tetraacetic acid (EDTA) and mono-, di-, and tri-salts thereof.
Most preferably, the acidic component is mono-2-(methacryloyloxy)ethyl maleate, maleic anhydride, 2-({N-[2-(2-Methylprop-2-enoyloxy)ethyl]carbamoyloxy}methyl)-3-[N-(2-prop-2-enoyloxyethyl)carbamoyloxy] propanoic acid (PDMA), poly(acrylic acid), ethylenediamine tetraacetic acid, and/or mono-, di-, and tri-salts of ethylenediamine tetraacetic acid. Most preferably, the poly(acrylic acid) has a molecular weight of about 2000. The structures of some of these preferred acidic components are shown below: 
A cationic initiator must be used in the composition of the present invention. Free radical initiators may also be used if a free radically polymerizable component is optionally included in the composition. The adhesive composition of the present invention can be photocured or chemically cured. The broad class of cationic initiators available in the industry, such as photoactive cationic nuclei, photoactive cationic moieties, and photoactive cationic organic compounds may be used in the composition of the present invention for photocuring. Cationic intiators such as HCl, HBr, HI, C6H5SO3H, HSbF6, HAsF6, HBF4, or Lewis acids, such as metal halide salts, may be used for chemically curing. Preferably, the adhesive composition ofthe present invention is photocured. More preferably, the initiator used in the adhesive composition of the present invention includes a diaryliodonium salt. If the initiator only includes a diaryliodonium salt, the adhesive must be cured with UV light. Preferably, the initiator also includes a photosensitizer so that the adhesive composition can be cured using visible light.
Most preferably, the initiator used in forming the polymerizable compositions of the presevt invention is a ternary system that includes a diaryliodonium salt, a sensitizer, and an electron donor compound. This system can function as a cationic and free radical initiator. This ternary photoinitiator system allows efficient cationic polymerization under conditions of room temperature and standard pressure, which permits its use with a variety of photopolymerizable compositions. Use of this ternary initiator system can provide a substantial reduction in the time required for the present compositions to cure to a tack-free gel or solid compared with systems that only contain a diaryliodonium salt and a photosensitizer. This reduction in gel time can in some cases represent about a 30 to 70% decrease in the time required for a resin composition to harden to a tack-free gel or solid. Still further, some compositions fail to polymerize altogether in the absence of an electron donor.
The first component ofthe preferred ternary photoinitiator system is an iodonium salt (PI), i.e., a diaryliodonium salt. The iodonium salt should be soluble in a monomer used to make the composition and preferably is shelf-stable, meaning it does not spontaneously promote polymerization when dissolved therein in the presence of the sensitizer and the electron donor compound, the second and third components of the preferred photoinitiator system. Accordingly, selection of a particular iodonium salt may depend to some extent upon the particular monomer, sensitizer and donor chosen. Suitable iodonium salts are described in U.S. Pat. Nos. 3,729,313; 3,741,769; 3,808,006; 4,250,053 and 4,394,403. The iodonium salt can be a simple salt, containing an anion such as Clxe2x80x94, Brxe2x80x94, Ixe2x80x94 or C6H5SO3xe2x80x94; or a metal complex salt containing an antimonate, arsenate, phosphate orborate such as SbF5OHxe2x80x94 or AsF6xe2x80x94. Mixtures of iodonium salts can be used if desired.
Aromatic jodonium complex salts of the structure below may be used as one of the components of the ternary photoinitiator system: 
wherein
Ar1 and Ar2 are aromatic groups having 4 to 20 carbon atoms and are selected from the group consisting of phenyl, thienyl, furanyl and pyrazolyl groups;
Z is selected from the group consisting of oxygen; sulfur; 
wherein R is aryl (of 6 to 20 carbons, such as phenyl) or acyl (of 2 to 20 carbons, such as acetyl, benzoyl, and the like); a carbon-to-carbon bond; or 
wherein R1 and R2 are selected from hydrogen, alkyl radicals of 1 to 4 carbons, and alkenyl radicals of 2 to 4 carbons;
n is zero or 1; and
X is a halogen-containing complex anion selected from the group consisting of tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, and hexafluoro anti monate.
The aromatic iodonium cations are stable and are well known and recognized in the art. See for example, U.S. Pat. Nos. 3,565,906; 3,712,920; 3,759,989; and 3,763,187; F. Beringer, et al., Diaryliodonium Salts IX, J. Am. Chem. Soc. 81,342-51 (1959) and F. Beringer, et al., Diaryliodonium Salts XXIII, J. Chem. Soc. 1964, 442-51; F. Beringer, et al., lodonium Salts Containing Heterocyclic Iodine, J. Org. Chem. 30, 1141-8 (1965); J. Crivello et al., Photoinitiated Cationic Polymerization with Triarylsulfonium Salts, J. Polymer Science, 17, 977 (1979).
Representative Ar1 and Ar2 groups are aromatic groups having 4 to 20 carbon atoms selected from phenyl, thienyl, furanyl, and pyrazolyl groups. These aromatic groups may optionally have one or more fused benzo rings (e.g., naphthyl and the like; benzothienyl; dibenzothienyl; benzofuranyl, dibenzofuranyl; and the like). Such aromatic groups may also be substituted, if desired, by one or more of the following non-basic groups which are essentially non-reactive with epoxide and hydroxy: halogen, nitro, N-arylanilino groups, ester groups (e.g., alkoxycarbonyl such as methoxycarbonyl and ethoxycarbonyl, phenoxycarbonyl), sulfo ester groups (e.g., alkoxylsulfonyl such as methoxysulfonyl and butoxysulfonyl, phenoxysulfonyl, and the like), amido groups (e.g., acetamido, butyramido, ethylsulfonamido, and the like), carbamyl groups (e.g., carbamyl, N-alkylcarbamyl, N-phenylcarbamyl, and the like), sulfamyl groups (e.g., sulfamyl, N-alkylsulfamyl, N,N-dialkylsulfamyl, N-phenylsulfamyl, and the like), alkoxy groups (e.g., methoxy, ethoxy, butoxy, and the like), aryl groups (e.g., phenyl), alkyl groups (e.g., methyl, ethyl, butyl, and the like), aryloxy groups (e.g., phenoxy)alkylsulfonyl (e.g., methylsulfonyl, ethylsulfonyl, and the like), arylsulfonyl groups (e.g., phenylsulfonyl groups), perfluoroalkyl groups (e.g., trifluoromethyl, perfluoroethyl, and the like), and perfluoroalkylsulfonyl groups (e.g., trifluoromethylsulfonyl, perfluorobutylsulfonyl, and the like).
Examples of useful aromatic iodonium complex salt photoinitiators include: diphenyliodonium tetrafluoroborate; di(4-methylphenyl)iodoniuti tetrafluoroborate; phenyl-4-methlphenyliodonium tetrafluoroborate; di(4-heptylphenyl)iodonium tetrafluoroborate; di(3-nitrophenyl)iodonium hexafluorophosphate; di(4-chlorophenyl)iodonium hexafluorophosphate; di(naphthyl)iodonium tetrafluoroborate; di(4-trifluoromethylphenyl)iodonium tetrafluoroborate; diphenyliodonium hexafluorophosphate; di(4-methylphenyl)iodonium hexafluorophosphate; dinphenyliodonium hexafluoroarsenate; di(4-phenoxyphenyl)iodonium tetrafluoroborate; phenyl-2-thienyliodonium hexafluorophosphate; 3,5-dimethylpyrazolyl-4-phenyliodonium hexafluorophosphate; diphenyliodonium hex afluoroantimonate; 2,2xe2x80x2-diphenyliodonium tetrafluoroborate; di(2,4-dichlorophenyl)iodonium hexafluorophosphate; di(4-bioniophenyl)iodonium hexafluorophosphate; di(4-methoxyphenyl)iodonium hextafluorophosphate; di(3-carboxyphenyl)iodonium hexafluorophosphate; di(3-methoxycarbonylphenyl)iodonium hexafluorophosphate; di(3-methoxysulfonylphenyl)iodonium hexafluorophosphate; di(4-acetamidophenyl)iodonium hexafluorophosphate; di(2-benzothienyl)iodonium hexafluorophosphate; (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate (OPIA) obtained from GE Silicones, 479-2092C; diphenyliodonium hexafluoroantimonate (DPISbF6); [4-(2-hydroxytetradecyloxyphenyl)]phenyliodonium hexafluoroantimonate (CD 1012) obtained from Sartomer SarCat CD-1012; and [4-(1-methylethyl)phenyl] (4-methylphenyl)iodonium tetrakis (pentafluorophenyl)borate(1xe2x88x92) (RHO 2074) obtained from Rhodia, Inc., Rhodorsil Photoinitiator 2074.
Of the aromatic iodonium complex salts which are suitable for use in the compositions of the invention, diaryliodonium hexafluorophosphate and diaryliodonium hexafluoroantimonate are among the preferred salts. Specific examples of such salts are (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate (OPIA), [4-(2-hydroxytetradecyloxyphenyl)]phenyliodonium hexafluoroantimonate, and [4-(1-methylethyl)phenyl] (4-methylphenyl)iodonium tetrakis (pentafluorophenyl)borate(1xe2x88x92). These salts are preferred because, in general, they are more thermally stable, promote faster reaction, and are more soluble in inert organic solvents than are other aromatic iodonium salts of complex ions.
The second component in the preferred ternary photoinitiator system is the photosensitizer (PS). Desirably, the photoinitiator should be sensitized to the visible spectrum to allow the polymerization to be initiated at room temperature using visible light. The sensitizer should be soluble in the photopolymerizable composition, free of functionalities that would substantially interfere with the cationic curing process, and capable of light absorption within the range of wavelengths between about 300 and about 1000 nanometers.
A sensitizer is selected based in part upon shelf stability considerations. Accordingly, selection of a particular sensitizer may depend to some extent upon the particular adhesive components, iodonium salt, and electron donor chosen.
Suitable sensitizers include one or more compounds in the following categories: ketones, courmarin dyes (e.g., ketocoumarins), xanthene dyes, acridine dyes, thiazole dyes, thiazine dyes, oxazine dyes, azine dyes, aminoketone dyes, porphyrins, aromatic polycyclic hydrocarbons, p-substituted aminostyryl ketone compounds, aminotriaryl methanes, merocyanines, squarylium dyes and pyridinium dyes. Ketones (e.g., monoketones or alpha-diketones), ketocoumarins, aminoarylketones, p-substituted aminostyryl ketone compounds, are preferred sensitizers. For applications requiring deep cure (e.g., cure of highly-filled composites), it is preferred to employ sensitizers having an extinction coefficient below about 1000 lmolexe2x88x921 cmxe2x88x921, more preferably about or below 100 lmolxe2x88x921 cmxe2x88x921, at the desired wavelength of irradiation for photopolymerization, or alternatively, the initiator should exhibit a decrease in absorptivity upon light exposure. Many of the alpha-diketones (alpha-dicarbonyl compounds) are an example of a class of sensitizers having this property, and are particularly preferred for dental applications.
By way of example, a preferred class of ketone sensitizers has the formula:
ACO(X)bB
where X is CO or CR1R2 where R1 and R2 can be the same or different, and can be hydrogen, alkyl, alkaryl or aralkyl, b is zero or one, and A and B can be the same or different and can be substituted (having one or more non-interfering substituents) or unsubstituted aryl, alkyl, alkaryl, or aralkyl groups, or together A and B can form a cyclic structure which can be a substituted or unsubstituted cycloaliphatic, aromatic, heteroaromatic or fused aromatic ring.
Suitable ketones ofthe above formula include monoketones (b=0) such as 2,2-, 4,4- or 2,4-dihydroxybenzophenone, di-2-pyridyl ketone, di-2-furanyl ketone, di-2-thiophenyl ketone, benzoin, fluorenone, chalcone, Michler""s ketone, 2-fluoro-9-fluorenone, 2-chlorothioxanthone, acetophenone, benzophenone, 1- or 2-acetonaphthone, 9-acetylanthracene, 2-, 3- or 9-acetylphenanthrene, 4-acetylbiphenyl, propiophenone, n-butyrophenone, valerophenone, 2-, 3- or 4-acetylpyridine, 3-acetylcoumarin and the like. Suitable diketones include aralkyldiketones such as anthraquinone, phenanthrenequinone, o- and p-diacetylbenzene, 1,3-, 1,4-, 1,5-, 1,6-, 1,7- and 1,8-diacetylnaphthalene, 1,5-, 1,8- and 9,10-diacetylanthracene, and the like. Suitable xcex1-diketones (b=1 and X=CO) include 2,3-butanedione, 2,3-pentanedione, 2,3-hexanedione, 3,4-hexanedione, 2,3-heptanedione, 3,4-heptanedione, 2,3-octanedione, 4,5-octanedione, benzyl, 2,2xe2x80x2- 3,3xe2x80x2- and 4,4xe2x80x2-dihydroxylbenzyl, furyl, di-3,3xe2x80x2-indolylethanedione, 2,3-bomanedione (camphorquinone), biacetyl, 1,2-cyclohexanedione, 1,2-naphthaquinone, acenaphthaquinone, and the like.
Examples of particularly preferred visible light sensitizers include (+/xe2x88x92) camphorquinone (CQ), 97%, Aldrich 12, 489-3; 2-chlorothioxanthen-9-one, Aldrich C7, 240-4; glyoxal; biacetyl; 3,3,6,6-tetramethylcyclohexanedi one; 3,3,7,7-tetramethyl-1,2-cycloheptanedione; 3,3,8,8-tetramethyl-1,2-cyclooctanedione; 3,3,18,18-tetramethyl-1,2-cyclooctadecanedione; dipivaloyl; benzyl; furyl; hydroxybenzyl; 2,3-butanedione; 2,3-pentanedione; 2,3-hexanedione; 3,4-hexanedione; 2,3-heptanedione; 3,4-heptanedione; 2,3-octanedione; 4,5-octanedione; and 1,2-cyclohexanedione. Most preferably, the photosensitizer is (+/xe2x88x92) camphorquinone.
The third component of the preferred photoinitiator system is one or more electron donor compounds (ED). These electron donor compounds act as reaction accelerators and accelerate the photopolymerization rate of adhesive composition. The electron donor compound(s) should meet the requirements set forth below and be soluble in the polymerizable composition. The donor can also be selected in consideration of other factors, such as shelf stability and the nature of the polymerizable materials, iodonium salt and sensitizer chosen. A class of donor compounds that may be useful in the inventive systems may be selected from some of the donors described in Palazzotto et al., U.S. Pat. No. 5,545,676. Possible donor compounds that meet the criteria set forth by Palazzotto et al. must then be tested using one or both of the methods set forth below to determine if they will be useful donors for the adhesive compositions of the present invention.
The donor is typically an alkyl aromatic polyether or an alkyl, aryl amino compound wherein the aryl group is optionally substituted by one or more electron withdrawing groups. Examples of suitable electron withdrawing groups include carboxylic acid, carboxylic acid ester, ketone, aldehyde, sulfonic acid, sulfonate and nitrile groups.
The suitability of a compound for use as an electron donor in the compositions of the invention may be determined by measuring the photoinduced potential of a sample photoinitiator system that includes the compound. The photoinduced potential can be evaluated in the following .O manner. A standard solution is prepared that contains 2.9xc3x9710xe2x88x925 moles/g of diphenyl iodonium hexafluoroantimonate and 1.5xc3x9710xe2x88x925 moles/g of camphorquinone (CQ) in 2-butanone. A pH electrode is then immersed in the solution and a pH meter is calibrated to zero mV. A test solution of the standard solution and the compound is prepared next using the compound at a concentration of 2.9xc3x9710xe2x88x925 moles/g. This test solution is irradiated using blue light having a wavelength of about 400 to 500 nm having an intensity of about 200 to 400 mW/cm2 for about 5 to 10 seconds at a distance of about 1 mm. Millivolts relative to the standard solution are then determined by immersing the pH electrode in the test solution and obtaining a mV reading on the pH meter. Useful donors are those compounds that provide a reading of at least 50 mV relative to the standard solution. Higher mV readings are generally indicative of greater activity.
In some instances there may be some uncertainty regarding the outcome of the above procedure. This may be due to questions or uncertainty arising from the instrumentation employed, from the way the procedure was carried out, or other factors, or one may wish to verify the suitability of a particular compound. A second test may be performed to verify the result obtained by following the above procedure and resolve any such uncertainty.
The second method involves the evaluation of the photoinduced potential of an initiator system that includes the compound compared to a system that includes N,N-dimethylaniline. For this method, a standard solution of 2.9xc3x9710xe2x88x925 moles/g diphenyl iodonium hexafluoroantimonate, 1.5xc3x9710xe2x88x925 moles/g camphorquinone (CQ) and 2.9xc3x9710xe2x88x925 moles/g of N,N-dimethylaniline in 2-butanone is prepared. A pH electrode is then immersed in the solution and a pH meter is calibrated to zero mV. The standard solution is irradiated with blue light having a wavelength of between about 400-500 nm and an intensity of about 200 to 400 mW/cm2 for about 5 to 10 seconds using a focused light source such as a dental curing light at a distance of about 1 mm. After light exposure, the potential of the solution is measured by immersing a pH electrode in the irradiated standard solution and reading the potential in mV using a pH meter. A test solution is then prepared using 2.9xc3x9710xe2x88x925 moles/g of diphenyl iodonium hexafluoroantimonate, 1.5xc3x9710xe2x88x925 moles/g ofcamphorquinone and 2.9xc3x9710xe2x88x925moles/g of the compound in 2-butanone. The test solution is irradiated and the photoinduced potential measured using the same technique as described for the standard solution. If the test solution has a photoinduced potential that is the same as or greater than that of the N,N-dimethylaniline containing standard solution, then the compound is a useful donor.
A preferred group of alkyl, aryl amine donor compounds is described by the following structural formula: 
wherein
each R1 is independently H; C1-8 alkyl that is optionally substituted by one or more halogen, xe2x80x94CN, xe2x80x94OH, xe2x80x94SH, C1-18 alkoxy, C3-18 alkylthio, C3-18 cycloalkyl, aryl, COOH, COOC1-18 alkyl, (C1-18 alkyl)0-1xe2x80x94COxe2x80x94C1-18 alkyl SO3R2; aryl that is optionally substituted by one or more electron withdrawing groups; or the R1 groups together may form a ring,
where R2 is H; C1-18 alkyl that is optionally substituted by one or more halogen, xe2x80x94CN, xe2x80x94OH, xe2x80x94SH, C1-18 akoxy, C1-18 alkylthio, C3-18 cycloalkyl, aryl, COOH, COOC1-18 alkyl, (C1-18 alkyl)0-1xe2x80x94COxe2x80x94C1-18 alkyl, or SO3H; and
Ar is aryl that is optionally substituted by one or more electron withdrawing groups. Suitable electron withdrawing groups include xe2x80x94COOH, xe2x80x94COOR2, xe2x80x94SO3R2, xe2x80x94CN, xe2x80x94COxe2x80x94C1-18 alkyl, and C(O)H groups.
A preferred group of aryl alkyl polyethers has the following structural formula: 
wherein n=1-3, each R3 is independently H or C1-18 alkyl that is optionally substituted by one or more halogen, xe2x80x94CN, xe2x80x94OH, xe2x80x94SH, C1-18 alkoxy, C1-18 alkylthio, C3-8 cycloalkyl, aryl, substituted aryl, xe2x80x94COOH, xe2x80x94COOC1-18 alkyl, xe2x80x94(C1-18 alkyl)0-1xe2x80x94COH, xe2x80x94(C1-18 alkyl)0-1xe2x80x94CO-C1-18 alkyl, xe2x80x94COxe2x80x94C1-18 alkyl, xe2x80x94C(O)H or xe2x80x94C2-8 alkenyl groups and each R4 can be C1-18 alkyl that is optionally substituted by one or more halogen, xe2x80x94CN, xe2x80x94OH, xe2x80x94SH, C1-18 alkoxy, C1-18 alkylthio, C3-18 cycloalkyl, aryl, substituted aryl, xe2x80x94COOH, xe2x80x94COOC1-18 alkyl, xe2x80x94(C1-18 alkyl)0-1xe2x80x94COH, xe2x80x94(C1-18 alkyl)0-1xe2x80x94COxe2x80x94C1-18 alkyl, xe2x80x94COxe2x80x94C1-18 alkyl, xe2x80x94C(O)H or xe2x80x94C2-18 alkenyl groups.
In each of the above formulas, the alkyl groups can be straight-chain or branched, and the cycloalkyl group preferably has 3 to 6 ring carbon atoms but may have additional alkyl substitutions up to the specified number of carbon atoms. The aryl groups may be carbocyclic or heterocyclic aryl, but are preferably carbocyclic, and more preferably are phenyl rings.
Preferred donor compounds include, but are not limited to, 4,4xe2x80x2-bis(diethylamino)benzophenone (BDEAB), 99+%, Acros 17081-0250; 4-dimethylaminobenzoic acid (4-DMABA); ethyl p-dimethylaminobenzoate (EDMAB), 99+%, Acros 11840-1000; 3-dimethylamino benzoic acid (3-DMABA); 4-dimethylaminobenzoin (DMAB); 4-dimethylaminobenzaldehyde (DMABAL); 1,2,4-trimethoxybenzene (TMB); and N-phenylglycine (NPG).
The compounds of the ternary photoinitiator system are provided in an amount effective to initiate or enhance the rate of cure of the resin system. It has been found that the amount of donor that is used can be critical, particularly when the donor is an amine. Too much donor can be deleterious to cure properties. Preferably, the sensitizer is present in about 0.05-5 weight percent based on resin compounds of the overall composition. More preferably, the sensitizer is present at about 0.10-1.0 weight percent. Similarly, the iodonium initiator is preferably present at about 0.05-10.0 weight percent, more preferably at about 0.10-5.0 weight percent, and most preferably at about 0.50-4.0 weight percent. Likewise, the donor is preferably present at about 0.01-5.0 weight percent.
An alternative photoinitiator system for cationic polymerization includes the use of organometallic complex cations essentially free of metal hydride ormetal alkyl functionality selected from those described in U.S. Pat. No. 4,985,340, and such description is incorporated herein by reference and has the formula:
[(L1)(L2)M]+q
wherein
M represents a metal selected from the group consisting of Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Pd, Pt and Ni, preferably Cr, Mo, W, Mn, Fe, Ru, Co, Pd, and Ni; and most preferably Mn and Fe;
L1 represents 1 or 2 cyclic, polyunsaturated ligands that can be the same or different ligand selected from the group consisting of substituted and unsubstituted cyclopentadienyl, cyclohexadienyl, and cycloheptatrienyl, cycloheptatriene, cyclooctatetraene, heterocyclic compounds and aromatic compounds selected from substituted or unsubstituted arene compounds and compounds having 2 to 4 fused rings, and units of polymers, e.g., a phenyl group of polystyrene, poly(styrene-co-butadiene), poly(styrene-co-methyl methacrylate), poly(a-methylstyrene), and the like; a cyclopentadiene group of poly(vinylcyclopentadiene); a pyridine group of poly(vinylpyridine), and the like, each capable of contributing 3 to 8 electrons to the valance shell of M;
L2 represents none, or 1 to 3 nonanionic ligands contributing an even number of electrons that can be the same or different ligand selected from the group of carbon monoxide, ketones, olefins, ethers, nitrosonium, phosphines, phosphites, and related derivatives of arsenic and antimony, organoitriles, amines, alkynes, isonitriles, dinitrogen, with the proviso that the total electronic charge contributed to M results in a net residual positive charge of q to the complex;
q is an integer having a value of 1 or 2, the residual charge of the complex cation.
Organometallic salts are known in the art and can be prepared as described in, for example, EPO No. 094,914 and U.S. Pat. Nos. 5,089,536, 4,868,288, and 5,073,476, and such descriptions are incorporated herein by reference.
Examples of preferred cations include:
bis(xcex75-cyclopentadienyl)iron(1+), bis(xcex75-methylcyclopentadienyl)iron (1+),
(xcex75-cyclopentadienyl)(xcex75-methylcyclopentadienyl)iron(1+), and bis(xcex75-trimethylsilylcyclopentadienyl)iron(1+);
bis(xcex76-xylenes)iron(2+), bis(xcex76-mesitylene)iron(2+), bis(xcex76-durene)iron(2+), bis(xcex76-pentamethylbenzene)iron(2+), and bis(xcex76-dodecylbenzene)iron(2+);
(xcex75-cyclopentadienyl)(xcex76-xylenes)iron(1+), commonly abbreviated as (CpFeXy)(1+),
xcex75-cyclopentadienyl)(xcex76-toluene)iron(1+),
xcex75-cyclopentadienyl)(xcex76-mesitylene)iron(1+),
xcex75-cyclopentadienyl)(xcex76-pyrene)iron(1+),
xcex75-cyclopentadienyl)(xcex76-naphthalene)iron(1+), and
xcex75-cyclopentadienyl)(xcex76-dodecylphenyl)iron(1+).
Still further, a variety of visible or near-IR photoinitiators may be used for photopolymerization of free-radically polymerizable materials in the composition of the present invention. Free-radical initiators useful in the invention, e.g., those that are photochemically active in the wavelength region of greater than 400 to 1200 nm, may include the ternary initiator system discussed above and the class of acylphosphine oxides, as described in European Patent Application No. 173567. Tertiary amine reducing agents may be used in combination with an acylphosphine oxide. Illustrative tertiary amines useful in the invention include ethyl 4-(N,N-dimethylamino)benzoate and N,N-dimethylaminoethyl methacrylate. The initiator can be employed in catalytically-effecitve amounts, such as from about 0.1 to about 5 weight percent, based on the weight of ethylenically-unsaturated compound present, of the acylphosphine oxide plus from about 0.1 to about 5 weight percent, based on the weight of ethylenically-unsaturated compound present, of the tertiary amine.
Commercially-available phosphine oxide photoinitiators capable of free-radical initiation when irradiated at wavelengths ofgreater than 400 nm to 1200 nm include a 25:75 mixture, by weight, of bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and 2-hydroxy-2methyl-1phenylpropan-1-one(IRGACURE(trademark) 1700, Ciba Specialty Chemicals),2-benzyl-2-(N,N-dimethylamino)-1-(4-morpholinophenyl)-1-butanone (IRGACURE(trademark) 369, Ciba Specialty Chemicals), bis(xcex75-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium (IRGACURE(trademark) 784 DC, Ciba Specialty Chemicals), a 1:1 mixture, by weight, of bis(2,4,6-trimnethylbenzoyl)phenyl phosphine oxide and 2-hydroxy-2-methyl-1-phenylpropane-1-one (DAROCUR(trademark) 4265, Ciba Specialty Chemicals), and ethyl-2,4,6-trimethylbenzylphenyl phosphinate (LUCIRN(trademark) LR8893X, BASF Corp., Charlotte, N.C.). Preferably, initiators such as Bisphenol A glycidyl methacrylate (BisGMA) and tributyl boron oxide (TBBO) are used to polymerize any free radically polymerizable materials included in the composition of the present invention.
Free-radical initiators useful in the invention, e.g., those that are photochemically active in the wavelength region of greater than 400 to 1200 nm, also may include the class of ionic dyexe2x80x94counterion complex initiators comprising a borate anion and a complementary cationic dye. Borate anions useful in these photoinitiators generally can be of the formula
R1R2R3R4Bxe2x88x92
wherein R1, R2, R3, and R4 independently can be alkyl, aryl, alkaryl, allyl, aralkyl, alkenyl, alkynyl, alicyclic and saturated or unsaturated heterocyclic groups. Preferably, R2, R3, and R4 are aryl groups and more preferably phenyl groups, and R1 is an alkyl group and more preferably a secondary alkyl group.
Cationic counterions can be cationic dyes, quaternary ammonium groups, transition metal coordination complexes, and the like. Cationic dyes useful as counterions can be cationic methine, polymethine, triarylmethine, indoline, thiazine, xanthene, oxazine or acridine dyes. More specifically, the dyes may be cationic cyanine, carbocyanine, hemicyanine, rhodaminel and azomethine dyes. Specific examples of useful cationic dyes include Methylene Blue, Safranine O, and Malachite Green. Quaternary ammonium groups useful as counterions can be trimethylcetylammonium, cetylpyridinium, and tetramethylammonium. Other organophilic cations can include pyridinum, phosphonium, and sulfonium. Photosensitive transition metal cordination complexes that may be used include complexes of cobalt, ruthenium, osmium, zinc, iron, and iridum with ligands such as pyridine, 2,2xe2x80x2 -bipyridine, 4,4xe2x80x2-dimethyl-2,2xe2x80x2-bipyridine, 1,10-phenanthroline, 3,4,7,8-tetramethylphenanthroline, 2,4,6-tri(2-pyridyl-s-triazine) and related ligands.
As discussed previously, a polyol may be added to the adhesive composition of the present invention as an optional component. Polyols that may be added include, but are not limited to poly(tetrahydrofuran) (PTHF) (preferably, average M=ca. 250, Aldrich 34, 526-1) and 2-oxepanone (polymer with 2-ethyl-2-(hydroxymethyl)-1,3-propane diol) obtained from Union Carbide under the tradename Tone 301. The preferred polyol for extending the gel-state during the photocure of the fonnulation is poly(tetrahydrofuran).
Optionally, an epoxy/polyol blend may be added to the adhesive composition in place of or in addition to the epoxy resin or other cationically polymerizable resin used in formulating the adhesive composition. Epoxy/polyol blends that may be added include, but are not limited to, Blend 4216-G: 42% GY281 and 42% UVR-6105 and 16% PTHF, Blend 4216-E: 42% Epon 825 and 42% UVR 6105 and 16% PTHF, Blend 4804-G: 48% GY 281 and 48% UVR 6105 and 4% PTHF, Blend 4804-E: 48% Epon 825 and 48% UVR 6105 and 4% PTHF, Blend 5000-G: 50% UVR 6105 and 50% GY 281, and Blend 5000-E: 50% UVR 6105 and 50% Epon 825.
As also discussed previously, a free radically polymerizable component may be added to the adhesive composition. This is a material having free radically active functional groups. A free radically active functional group refers to a chemical moiety that is activated in the presence of an initiator capable of initiating free radical polymerization such that it is available for reaction with other compounds bearing free radically active functional groups. The free radically polymerizable component can be made of monomers, oligomers, and polymers having one or more ethylenically unsaturated groups. Suitable materials contain at least one ethylenically unsaturated bond, and are capable of undergoing addition polymerization.
Suitable free radically-polymerizable monomers may contain at least one ethylenically-unsaturated bond, can be oligomers or polymers, and are capable of undergoing addition polymerization. Such monomers include mono-, di- or poly- acrylates and methacrylates such as methyl acrylate, methyl methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexyl acrylate, stearyl acrylate, allyl acrylate, glycerol diacrylate, glycerol triacrylate, ethyleneglycol diacrylate, diethyleneglycol diacrylate, triethyleneglycol dimethacrylate, 1,3-propanediol diacrylate, 1,3-propanediol dimethacrylate, trimethylolpropane triacrylate, 1,2,4-butanetriol trimethacrylate, 1-4-cyclohexanedio diacryl ate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, sorbitol hexacrylate, bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane, bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane, tris(hydroxyethylisocyanurate)trimethacrylate; the bis-acrylates and bis-methacrylates ofpolyethylene glycols of molecular weight 200-500, copolymterizable mixtures of acrylated monomers such as those of U.S. Pat. No. 4,652,274, incorporated herein by reference, and acrylated oligomers such as those of U.S. Pat. No. 4,642,126, incorporated herein by reference; unsaturated amides such as methylene bis-acrylamide, methylene bis-methacrylamide, 1,6-hexamethylene bisacrylamide, diethylene triamine tris-acrylamide and beta-methacrylaminoethyl methacrylate; and vinyl compounds such as styrene, diallyl phthalate, divinyl succinate, divinyl adipate and divinylphthalate. Mixtures of two or more monomers can be used if desired. Preferably, the free radically polymerizable material used is mono-, di-, or poly-acrylates and methacrylates such as methyl acrylate, methyl methacryle, ethyl acrylate, glycidyl methacrylate, 2-isocyanatoethyl methacrylate, limonene oxide, isopropyl methacrylate, n-hexyl acrylate, stearyl acrylate, allyl acrylate, glycerol diacrylate, glycerol triacrylate, ethyleneglycol diacrylate, diethyleneglycol diacrylate, triethyleneglycol dimethacrylate, 1,3-propanediol diacrylate, 1,3-propanediol dimethacrylate, trimethylolpropane triacrylate, 1,2,4-butanetriol trimethacrylate, 1,4-cyclhexanediol diacrylate, penterythritol triacrylate, pentaerythritol tetracrylate, pentaerythritol tetramethacrylate, sorbitol hexacrylate, bis[1-929acryloxy)]-p-ethosyphenyl dimethylmethane, bis[1-(3-acryloxy-2-hydroxy)}-p-propoxyphenyldimethylmethane, and trihydroxyethyl-isocyanurate trimethacrylate; the bisacrylates and bis-methacryles of polyethylene glycols of molecular weight 200-500, copolymerizable mixtures of acrylated monomers such as those in U.S. Pat. No. 4,652,274, and acrylated oligomers such as those of U.S. Pat. No. 4,642,126; and vinyl compounds such as styrene, diallyl phthalate, divinyl succinate, divinyl adipate and divinylphthalate. Mixtures of two or more of these free radically polymerizable materials can be used if desired.
As also discussed previously, a compound with a reactive olefinic moiety may also be included in the adhesive formulation. This reactive olefinic moiety may be located on the acidic component or may be a separate compound. Some of the preferred acidic components listed above include reactive olefinic moieties thereon.
Still further, this composition may include multi-functional compounds that contain several of the functional groups discussed above combined in the same molecule. For example, a compound may contain cationically and free radically polymerizable groups in the same molecule. This composition may also include combinations of each of the components discussed above.
The adhesive composition of the present invention should include about 10-99 wt % cationically polymerizable component, about 0.1-30 wt % acidic component, and about 0.1-10 wt % of the initiator that is capable of initiating cationic polymerizaiton. All percentages of components throughout this application are weight percentages unless otherwise noted. It also may contain up to about 90% of the optional free radically polymerizable component, up to about 20% of a polyol, and up to about 90% compounds containing olefinic moieties other than acidic components containing olefinic moieties. Preferably, the adhesive composition includes about 75% cationically polymerizable component, about 20% acidic component, and about 5% initiator capable of initiating cationic polymerization.
Preferred formulations of the adhesive compositions of the present invention include those listed in Examples 4, 7, 11, 14, 18, 22, 24, 26, 30, 32, 34, 36, 38, 40, 41, 42, 44, 46, 49, 52 and 54. Most preferably, the adhesive compositions of the present invention are the formulations disclosed in Examples 24, 49, 52 or 54. The percentages of components discussed infra do not account for the amount of initiator in the formulation. The first of these most preferred formulations includes 45.6% Epon 825,45.6% UVR 6105,3.8% pTHF, and 5.0% maleic anhydride. The second of these most preferred formulations includes 38.4% Epon 825, 38.4% UVR 6105, 3.2% pTHF, and 20.0% MAEM. The third ofthese most preferred formulations includes 26.88% Epon 825,26.88% UVR 6105, 2.24% pTHF, 24.0% HEMA, and 20.0% MAEM. The fourth of these most preferred formulations includes 38.4% UVR 6105, 38.4% GY 281, 3.2% Heloxy 48, and 20.0% MAEM.
The adhesive composition of the present invention can be adhered to any hard tissue. It is especially useful in dental formulations for adhesive bonding of cationically polymerizable dental restorative materials to dentin and enamel substrates. Still further, it is able to bond to dental metals, ceramics, and composites. It is also useful as a dental material for sealing cracks and fissures in tooth structures and in cationically curable tooth restorative materials. This adhesive is a cationically initiated adhesive which is compatible with a cationically photoinitiated dental restorative system and is capable of bonding the dental restorative to the tooth substrate. Preferably, it has a bond strength to hard tissue of at least about 10 kg/cm2.
The adhesive composition of the present invention is applied in the form of a relatively thin layer to a hard tissue surface. Examples of hard tissue surfaces include teeth (the component parts of which are enamel, dentin, and cementum), bone, fingernails, and hoofs. Prior to application of the adhesive composition, the hard tissue surface may be pre-treated or primed to enhance adhesion to the hard tissue surface (e.g., using an acid etchant, primer, and/or adhesion promoter).
Following application to the hard tissue surface the adhesive composition is preferably polymerized to form an adhesive layer on the hard tissue surface. Polymerization takes place by exposing the adhesive composition to polymerizable conditions sufficient to form a hardened composition adhered to the hard tissue. Preferably, polymerization is effected by exposing the adhesive composition to a radiation source, preferably, a visible light source. Suitable visible light sources include a Visilux(trademark) dental curing light commercially available from 3M Company of St. Paul, Minn. Such lights have an intensity of about 200-700 mW/cm2 at a wavelength of 400-500 nm.
Following polymerization to form the cured adhesive, a second composition may be applied to the adhesive. The adhesive compositions are particularly useful for bonding dental compositions, especially where the dental composition contains cationically active functional groups such as epoxy groups or vinyl ether groups. The dental compositions may be filled or unfilled, and include dental materials such as direct esthetic restorative materials (e.g., anterior and posterior restoratives), prostheses, sealants, veneers, cavity liners, crown and bridge cements, artificial crowns, artificial teeth, dentures, and the like. In the case of dental compositions containing cationically active functional groups, the dental composition is polymerized via a cationic mechanism following application to the bonding adhesive composition of the present invention.
In an alternate embodiment of the present invention, additional acidic component is applied to the hard tissue before the adhesive composition is applied to the hard tissue. The acidic component may be applied as a neat liquid, in a concentrated solution, or with a solvent, such as acetone, ethanol or HEMA. In still another alternative embodiment, the adhesive composition is formed on the substrate by first applying an acidic component to the substrate, subsequently applying a cationically polymerizable component and corresponding initiator, and then curing these layers.
The term xe2x80x9ccompositexe2x80x9d as used herein refers to a filled dental material. The term xe2x80x9crestorativexe2x80x9d as used herein refers to a composite which is polymerized after it is disposed adjacent to a tooth. The term xe2x80x9cprosthesisxe2x80x9d as used herein refers to a composite which is shaped and polymerized for its final use (e.g., as crown, bridge, veneer, inlay, onlay, or the like) before it is disposed adjacent to a tooth. The term xe2x80x9csealantxe2x80x9d as used herein refers to a lightly filled composite or to an unfilled dental material which is polymerized after it is disposed adjacent to a tooth. xe2x80x9cPolymerizablexe2x80x9d refers to curing or hardening the dental material, e.g., by cationic or cationic and free-radical mixed reaction mechanisms.
The advantage of the adhesive composition of the present invention is that it demonstrates enhanced composite-to-tooth substrate bonding levels compared to corresponding formulations not containing an acidic component. The compositions ofthe present invention enable a cationically rich or even cationically pure system to cure to a solid mass. This composition is able to cationically cure at the interface of a tooth""s surface. The acidic components used in the adhesive composition ofthe present invention enhance the bonding of cationic restoratives to tooth substrates by undergoing physicochemical interactions with hard tissue. The adhesive compositions of the present invention successfully polymerize on the surface of hard tissue to bond with the hard tissue, yet at the same time, can successfully bond to compositions that include cationically active groups. In one embodiment of the present invention, after the adhesive composition is applied to the hard tissue and exposed to polymerization conditions, a second polymerizable composition comprising a cationically active functional group and a polymerization initiator capable of initiating cationic polymerization is applied, and it is exposed to polymerization conditions to form a hardened composition adhered to the hard tissue.
Another embodiment of the present invention is a dental restorative material that is comprised of a cationically polymerizable component, an acidic component, an initiator capable of initiating cationic polymerization such as the ternary photoinitiator discussed above, and a dental filler that does not substantially interfere with cationic polymerization in an amount of between about 10 to 90% by weight based on the total weight of the dental restorative material.
A further embodiment of the present invention is a kit comprising the adhesive composition of the present invention and an instruction sheet for the application of the adhesive composition to hard tissue. Preferably, the kit also includes a dental material capable of bonding to the adhesive. Preferably, the dental material is a dental metal, a ceramic, a composite, or a dental restorative material that comprises a mixture of a cationically polymerizable component, an acidic component, an initiator capable of initiating cationic polymerization, and a dental filler that does not substantially interfere with cationic polymerization in an amount of between about 10 to 90% by weight based on the total weight of the dental restorative material. The kit may further include one or more pre-treatment materials selected from the group consisting of etchants, primers, adhesion promoters, and combinations thereof.